The present invention relates to the manufacture of fibrous sheet materials such as paper, cardboard, nonwoven materials and more specifically it relates to the method of their manufacture.
Known in the art is an aerodynamic method of manufacturing fibrous materials consisting in that the fibrous raw material with an absolute moisture content of 5 to 100% and over of the weight of absolutely dry fibres which amounts to 95-50% and less in terms of concentration of fibres in the mass is preliminarily dispersed into individual fibres which are introduced into a stream of air for producing an air-material mixture in the form a directional flow delivered onto the moving screen of a moulding chamber.
Then the fibres are distributed over the screen by mechanical atomization of the mixture. The fibrous material is moulded on the moving screen by settling the fibres from the air-material mixture under the effect of pressure difference above and under the screen.
After producing a uniform layer of the fibrous material on the moving screen, said layer is mechanically compacted. Then the compacted material is dried and finished.
Owing to a high concentration of the source fibrous material (95-50%) the known method fails to generate the required amount of stream for dispersing the compacted fibre clots in the process of conveying the air-material mixture into the moulding chamber. Hence, the known method does not ensure a high degree of dispersion and distribution of fibres in the stream. This disadvantage in turn impairs the quality of the finished fibrous material which is characterized by an insufficiently uniform distribution of fibres and, as a consequence, by a low tensile strength. This also leads to a low speed of material moulding, a low output of the production equipment and a limited number of manufactured products. Thus, the known method can be utilized for manufacturing cardboard only.
There have been attempts made to eliminate the aforesaid disadvantages. A method has been envolved which has raised the uniformity of distribution fibres in the manufactured sheet material and increased its tensile strength. The source material in this method has been wood pulp subjected to mechanical and thermal treatment at 100.degree. C. and higher to a moisture content of 30% and above (concentration of fibres in the mass being 70% and less).
The mass with the above-specified moisture content is distributed in a stream of gas thus producing an air-material mixture which is then directed into a moulding chamber and moulded similarly to the method described above.
In our opinion, the thermal treatment of the fibrous raw material in the above-described method equalizes the variations in the wetness of fibres in the moulding chamber which has a positive effect on the more uniform distribution of fibres in the chamber and in the finished fibrous sheet material. This in turn improves somewhat the tensile strength of the material.
However, in view of a relatively low wetness of the fibrous raw material this method is not quite efficient for producing fibrous materials with a high tensile strength and obtaining a high moulding speed.
Besides, both methods described above are rather complicated since they involve a number of individual successive operations such as dispersing the fibres, forming an air-material mixture and distributing the fibres in said mixture.